What makes an online community feel like a community?

Not the number of members, I think.

I've been in huge communities where you could post something and it would disappear immediately.

Then there are tiny ones where people somehow know each other.

Someone asks a question and people actually answer.

Someone posts something interesting and it turns into a conversation.

Nobody is trying to sell you something every 5 minutes.

Those places are rare.

And I'm not sure you can fake it either. Once a community starts feeling like an audience, people notice.